With current mobile telecommunications systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architecture, network node selection, reselection and handover is carried out on the basis of measurements of downlink signals broadcast by each of the network nodes. These measurements are performed by terminal devices (also known as user equipment or UEs), and network node selection, reselection or handover is then performed on the basis of these measurements so as to allow each UE to communicate with the network. Each network node may be, for example, a base station or a relay node.
The performance of such measurements (together with the associated measurement report signalling, handover signalling, reselection evaluation, etc.), however, results in high power consumption by the UE and requires the UE to comprise relatively complex and costly equipment for performing such measurements (which must be made over a range of different radio frequencies). This results in lower UE battery life, and also makes it difficult to design lower cost, simple UEs that are able to effectively communicate with a telecommunications network. In addition, these procedures require a significant amount of overhead in terms of control signalling between the UE and the network. For example, during handover several messages must be exchanged between the UE and the network before a handover can be considered complete (at least a measurement control, measurement report, handover, handover complete). This overhead associated with handover not only increases the signalling load in the network, but it also increases the probability of handover failure, particularly in the case of small cells and/or fast moving UEs, because of the time taken to perform the measurements and signalling.
Furthermore, in order to track the UE's location in idle mode, the UE must perform a location or tracking area update when moving to a different area of the network, and the network must page via all possible cells in the location or tracking area—this is a compromise between increased signalling due to frequent location/tracking area updates (e.g. if this was required on every cell change) and paging load within a location/tracking area to reach the UE whose location is not known at per-cell level, but only per location/tracking area.
The present invention aims to alleviate these problems.